A preponderant number of applications which entail the use of coal tar or petroleum pitches require the carbonization of the pitch material. Examples of carbonization processes include coking and graphitization. During the carbonization process, it is normal to lose between 25 and 65% of the binder, the exact loss being dependent on the volatile content of the pitch. The loss of volatiles to the environment is additionally undesirable in that they constitute a source of air pollution. It is common practice in the industry to indicate this weight loss by the fraction of the starting material which remains upon carbonization, eg. the fraction of the material remaining upon coking is called the "coking value" of the pitch. This characteristic is particularly important if the pitch is to be used as a binder for coke filler in the formation of coked carbon bodies.
A problem encountered with baked carbon bodies obtained from pitches is their relatively high oxidation rate, which is particularly noticeable when they are used as refractory materials or as electrodes. This oxidation rate can be attributed to such factors as the porosity of the can be attributed to such factors as the porosity of the carbon body, its specific surface and the inorganic impurities present in the carbon body.
Techniques hitherto employed to decrease this oxidation rate include pressure impregnation or coating of previously baked carbon bodies with aqueous solutions of oxidation retardant materials such as phosphates, silicates, etc., after which the carbon bodies are rebaked to drive away the moisture. While the former technique requires pressure treating equipment and large volumes of an often expensive impregnant, neither technique succeeds in inhibiting oxidation throughout the interior of the carbon body.
It is also known (British Pat. No. 865,320) to add oxidation inhibitors to the coke filler-pitch mix before baking. This technique has the disadvantage of requiring large amounts (4 to 20 parts by weight of the additive to 100 parts by weight of the corresponding mix) of the additive, which is expensive in comparison to the base material being treated. Such large amounts of additive can also have a deleterious effect if the carbon body resulting upon baking this mix, is used as an electrode. Additionally, the additive, normally being incombustible constitutes a substantial portion of the electrode which can contaminate the product as the electrode is consumed should any residue be left behind.
It is therefore the object of the present invention to provide a pitch composition, which upon carbonization yields a carbon body having improved oxidation resistance.